a shop selling paraphernalia of interest to drug users or associated with the use of drugs.
Origin of head shop
An Americanism dating back to 1965–70
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Word Origin and History for head shop
emporium for stoner gear, by 1969 (noted in 1966 as the name of a specific shop in New York City selling psychedelic stuff), from head (n.) in the drug sense.
Online Etymology Dictionary, © 2010 Douglas Harper